<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>变量</title>

    <script >

        //定义变量
       /* var a  = 3;
        alert(a);

        a = "abc";
        alert(a);*/

       //定义number类型

        var num = 1;
        var num2 = 1.2;
        var num3 = NaN;

        //输出到页面上
        document.write(num+"---"+typeof(num)+"<br>");
        document.write(num2+"---"+typeof(num2)+"<br>");
        document.write(num3+"---"+typeof(num3)+"<br>");

        //定义string类型

        var str = "abc";
        var str2 = 'edf';
        document.write(str+"---"+typeof(str)+"<br>");
        document.write(str2+"---"+typeof(str2)+"<br>");

        //定义boolean
        var flag = true;
        document.write(flag+"---"+typeof(flag)+"<br>");

        // 定义null,undefined
        var obj = null;
        var obj2 = undefined;
        var obj3 ;
        document.write(obj+"---"+typeof(obj)+"<br>");
        document.write(obj2+"---"+typeof(obj2)+"<br>");
        document.write(obj3+"---"+typeof(obj3)+"<br>");

    </script>


</head>
<body>

</body>
</html>